Production of titanium



March 14, 1961 I L. J. REIMERT ETAL PRODUCTION OF TITANIUM Filed March 19. 1958 lNV ENTORS LAWRENCE J. REIMERT ERASTUS A.FATZINGER 7 BY 7 /M, M W,%W

ATTORN United States Patent 2,975,111 PRODUCTION OF TITANIUM Lawrence J. Reimert, Schnecksville, and Erastus A. Fatzinger, Palmerton, Pa., assiguors to The New Jersey Zinc Company, New York, N.Y., a corporation of New Jersey Filed Mar. 19, 1958, Ser. No. 722,408

5 Claims. (Cl. 204-64) pursuant to the method of that application, by (1) supply-- ing the titaniferous source material, titanium tetrachloride, to the portion of the cell bath which is adjacent this distal surface of the cathode, (2) providing a com municating passageway between the aforementioned bath portion and the portion of the bath between the anode and cathode, this passageway providing direct communication between both portions of the bath but being small enough to retard difiusion of titanium ions from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface, and (3) maintaining a cell voltage sufficient to maintain depletion of titanium ions in the portion of the bath between the anode and proximate cathode surface such as to establish a back electromotive force within the range of about 2.6 to 3.4 Volts between the anode and cathode. This operation is characterized by the fact that the cell produces metallic titanium with high current efficiency and without any physical barrier, such as a diaphragm, between the anode and cathode.

In practice of the aforementioned method, a drop in the back electromotive force to as low as 2.4 volts was indicative of an excessive diffusion of titanium ions into the portion of the cell bath between the anode and cathode and was remedied by increasing the cell current. On the other hand, a rise in back electromotive force above 3.4 volts was accompanied by decomposition of nontitaniferous components of the bath and was remedied by decreasing the cell current. However, we have found that it is increasingly more difficult to establish the aforementioned electrolyzing conditions as the scale of the electrolyzing cell is increased. This is particularly characteristic of the starting-up phase of the cell oper ation in which the desired electrolyzing conditions are established. In particular, We have found it to require an extremely delicate balance of feed and current conditions in order to build up a sufficient concentration of titanous chlorides in the vicinity of the distal cathode surface to permit efficient electrolysis without causing such diffusion of the titanous chlorides into the bath between the anode and cathode as to lose control of the requisite back electromotive force between the anode and cathode.

We have now found that it is possible to build up and maintain the desired concentration, and relative proportions, of titanous chlorides in the vicinity of the distal surface of the deposition cathode, regardless of the size of the cell, by using an auxiliary cathode in contact with that portion of the bath which is in contact with the distal surface of the deposition cathode. In order to attain these results, We have found that the auxiliary cathode must be operated with a current density maintained, as hereinafter explained, sufliciently low to pre- 2,975,111 Patented Mar. 14, 1961 vent titanium deposition but sufiiciently high to eficct electrolytic reduction of titanium trichloride totitanium dichloride. The cell Wall itself is useful as the auxiliary cathode, but a separate cathode structure is particularly effective either in lieu of or in addition to the cell wall as the auxiliary cathode.

Accordingly, the improvement of our present invention comprises (a) eflecting circulation of the, bath in contact with the deposition cathode so as to maintain substantially uniform concentrations of the titanium trichloride and titanium dichloride in all portions of the bath which are adjacent and make contact with the deposition cathode and the auxiliary cathode, the auxiliary cathode being in direct communication with the deposition cathode through the medium of the bath therebetween, (b) distributing the electrolyzing current between the deposition and auxiliary cathodes so as to maintain substantially different current densities thereat, the current density at the auxiliary cathode being such as to effect electrolytic reduction of titanium trichloride to titanium dichloride but insufiicient to develop such polarization as to effect significant electrolytic reduction of titanium dichloride to metallic titanium.

The molten salt baths which are useful in practicing our invention comprise one or more of the halides of the alkali metals and alkaline earth metals. Thus, the chlorides, bromides, iodides and fluorides of sodium, potassium and lithium as well as the same halides of calcium, magnesium, barium and strontium may be used with advantage. However, in the interest of simplifying the recovery of the halogen which is liberated at the anode during electrolysis, we presently prefer to use only the chlorides of these metals. Although an individual halide may be used as a single constituent ba-th, wenow prefer to use a combination of these halides inasmuch as such combinations are characterized by relatively lower melting points than the individual salts. It is particularly advantageous, when using a combination of the aforementioned halides, to mix these halides in pro portions approximating a eutectic composition in order to obtain baths with low melting points. For example, we have used with particularly satisfactory results a eutectic mixture composed of 5 mol percent of sodium.

chloride, 40 mol percent of potassium chloride and 55 mol percent of lithium chloride, the resulting mixture having a melting point of about 345 C. Other useful eutectic mixtures are represented by the mixture composed of 48.5 mol percent of sodium chloride and 51.5 mol percent of calcium chloride having a melting point of 505 C. and by the mixture composed of 24 mol percent of barium chloride, 35 mol percent of sodium chloride and 41 mol percent of potassium chloride having a melting point of 552 C. Of course, as in all other molten salt electrolytic methods for the production of metallic titanium, the bath should be as completely anhydrous as possible and should be compounded of salts of high purity.

A content of titanium ions having a valence of less than four, i.e. titanous ions, may be established in such a molten salt bath by any one of a number of procedures. For example, titanium dichloride from an extraneous source may be introduced directly into the bath. On the other hand, the titanium dichloride may be formed in situ in the bath by dispersing finely divided metallic titanium throughout the bath and by then bubbling titanium tetrachloride into the bath so that, as a result of the reaction between the metallic titanium and the titanium tetrachloride, titanium dichloride is formed in the bath. However, the method of our present invention makes it particularly advantageous to establish the requisite lower valence titanium content of the bath without any danger of loss of control of electrolyzing conditions by introducing titanium tetrachloride directly into the bath while maintaining the aforementioned electrolyzing conditions. Regardless of the source of the titanium dichloride, its presence in the molten halide salt bath in amount of at least about 0.1% by Weight of the bath imparts to the bath the characteristic ofreadily assimilatingtitanium tetrachloride when the latter is brought into contact with the bath.

The titanium tetrachloride is advantageouslysupplied to the bath by introducing it directly into the molten bath either with or without a carrier gas such as argon. The cell atmosphere should, of course, be compartmented to maintain separation between the atmosphere above the portion of the bath into which the titanium tetrachloride is introduced and the portion of the bath from which the chlorine is evolved at the anode. Moreover, the cell is advantageously tightly closed in order to control the .cell atmosphere.

The cell electrodes should, of course, be constructed of material which will not introduce extraneous elements into the fused bath. Thus, a nonnietallic anode such as graphite or carbon should be used, graphite having been found in practice to be wholly suitable for this purpose. Cathodes and cell walls of nickel, and preferably of corrosion-resistant nickel base alloys, are useful in practicing the invention. At the prevailing cell temperature, the aforementioned cathode materials have been found not to contaminate the deposited metallic titanium to any significant degree and may be used in solid or foraminous form.

The relative position between, and the arrangement of, the anode and cathode within the molten salt body should be such that (a) chlorine evolved at the anode will rise in the body of molten bath without entering the body of molten bath adjacent the distal surface of the cathode, (b) the body of molten bath between the anode and the proximate cathode surface and the body of molten bath adjacent the distal surface of the cathode are in communication with one another through a multiplicity of passages, and (c) the distance between the anode and the proximate cathode surface, and hence the resistance of the bath between these surfaces, is sufficiently small to permit electrolytically induced depletion of the titanium content of the molten bath between these surfaces.

A number of arrangements of anode and cathode will assure these conditions, and a variety of such arrangements is shown in the drawings in our aforementioned application. However, a presently preferred cell arrangement for practicing the invention is shownin the accompanying drawing in which the single figure is a partial sectional elevation of the cell.

As shown in the drawing, a closed cell 1 is provided with a fused salt bath 2 in which a cylindrical cathode is preferably but not necessarily immersed. The deposition cathode comprises a cylindrical side wall body portion 3 closed at its lower end withan impervious bottom wall 4 but open at its top end. The side wall portion 3 is composed advantageously of sheet material having large openings 5 punched at intervals throughout its surface and having a lining of screen material 6 secured to the inner surface of the side wall portion. The impervious bottom wall and side wall portions are constructed of sheet metal composed of a corrosion-resistant nickel-base alloy, and the pervious screen 6 is constructed advantageously of Dutch weave wire mesh screen of the same alloy, the screen having 14 mesh per inch in one direction and 120 mesh per inch in the other direction. Other wire screens ranging from as coarse as 8 mesh to as fine as calendered wire filter cloth can be used effectively in the cathode construction. This deposition cathode structure is secured to a supporting rod 7 which projects into the cell through the cell roof and which thus .provides an electrical connection from an external source to the cathode structure positioned-within the cell. The cathode assembly thus encloses an inner body portion A of the fused salt bath 2.

The anode assembly for the cell comprises a silica dome 8 extending downwardly into the interior of the side walls 3 of the cathode assembly, the lower extremities of the dome being immersed in the fused salt bath 2. The dome is secured to a graphite anode base 9 which is provided with ports 19 and a depending anode section 11 whichis screwed into the anode base. The ports 10 permit escape of chlorine gas from the surface of the bath within the dome 8 into a chlorine efiluent tube 12 which extends through the roof of the cell. The roof of the cell is also provided with a titanium tetrachloride inlet line 13 so as to supply the tetrachloride to the lower portion of the main body portion B of the fused salt bath 2.

A separate auxiliary cathode structure is positioned in the main body portion B of the fused salt bath. This structure comprises advantageously a cylindrical body portion 14 supported by a current carrying rod 15 extending into the cell through the cell roof. The body portion of the auxiliary cathode is preferably formed with a relatively large surface area and this has been accomplished in practice by constructing the body portion 14 of wire screen made of 0.08 inch nickel wire and having 4 meshes per lineal inch. However, other types of foraminous conducting material can be used effectively for the auxiliary cathode provided that the openings in the material are not so fine that they will be blocked by small amounts of titanium metal inadvertently deposited on the material during cell operation. And, as mentioned previously, the smooth-surfaced, or even a corrugated surfaced, cell wall is elfective as an auxiliary cathode.

In the cell arrangement just described, the chlorine evolved at the anode leaves the surface of the bath within the confines of the silica dome 8 which thus define a compartment C in the cell atmosphere containing the evolved chlorine. The portion of the cell atmosphere exterior of this chlorine compartment defined by the walls comprises a compartment D into or through which titanium tetrachloride, with or without an inert carrier gas such as argon may be introduced. It will be seen, accordingly, that the titanium tetrachloride is absorbed by the body portion B of the bath so that it is added only to that portion of the bath in contact with the auxiliary cathode and with the distal surface of the deposition cathode. The body portion A of the bath, on the other hand, is maintained substantially completely depleted of titanium ions by control of the electrolyzing conditions. The unabsorbed argon is withdrawn from compartment D through an exit line 16 in the cell roof.

The electrolyzing condition which assures the maintenance of titanium-depletion in the .body portion A of the molten bath between the anode and the proximate cathode surface comprises the use of a voltage sufiiciently high to strip the body portion A of the bath substantially completely of its titanium chloride content. When the body portion A is efiectively stripped of its titanium chloride content, thus leaving essentially onlythe aforementioned eutectic bath composition composed of lithium, sodium and potassium chlorides, we have found that the back electromotive force of a specific cell structure, when measured across the anode and cathode upon opening of the exterior cell circuit, has a magnitude of about 2.6 volts or more when operating with a bath temperature of about 550 C. A back electromotive force below about 2.2 volts, in this cell, is an indication of the presence of-titanium chloride in the body portion A. As an upper limit of about 3.4 volts-is exceeded in this cell, and particularly as the back electromotive force reaches about 3.5 volts, decomposition of the non-titaniferous bath components such as the alkali metal chlorides begins to occur. It must be understood, and it will be readily appreciated by one skilled in the art of fused salt electrolysis, that the minimum and maximum back electromotive force will be influenced by the bath composition,

by the electrode compositions, by the bath temperature and by cell geometry. The back electromotive force is maintained so as to maintain appropriate depletion of titanium ions in the body portion A of the bath either by control of the cell voltage, or, as described in the copending application of Earl W. Andrews, Serial No. 628,117, now abandoned, by controlling the rate at which the titanium tetrachloride is delivered to the cell for assimilation by the molten bath. Measurement of the back electromotive force at intervals of 15 minutes is generally sufliciently frequent to permit the maintenance of a substantially uniform back electromotive force to within about one-tenth of a volt.

The electrolyzing condition which assures the establishment and maintenance of the desired concentration and relative proportions of titanium dichloride and titanium trichloride in the main body portion B of the molten bath comprises the maintenance of substantially different current densities at the deposition cathode and at the auxiliary cathode or cathodes. At the deposition cathode, polarization causes the surface-to-bath potential to rise to the point where decomposition of titanium dichloride is attained with resulting electrolytic reduction of the dichloride to titanium metal. The same result would be attained at the auxiliary cathode if the same current density prevailed at this cathode, assuming the bath composition to be substantially the same adjacent both cathodes. However, we have found that if a significantly lower current density is maintained at the surface of the auxiliary cathode, it is possible to effect electrolytic reduction of titanium trichloride to titanium dichloride at the auxiliary cathode without substantial reduction of the titanium dichloride to titanium metal. That is, by maintaining a lower current density at the auxiliary cathode than at the deposition cathode when both are in contact with the same titanous chloride containing bath, the polarization which develops at the auxiliary cathode will be less than that required to build up the surfaceto-bath potential to the level at which titanium dichloride is reduced to titanium metal. Consequently, the auxiliary cathode effects reduction of titanium trichloride to titanium dichloride, the incoming titanium tetrachloride reacts with some of the titanium dichloride to form titanium trichloride, and the remainder of the titanium dichloride is reduced to titanium meta at the deposition cathode.

The diflerence between the cathode surface-to-bath potential required to reduce titanium dichloride to titanium metal and that required to reduce titanium trichloride to titanium dichloride is approximately 0.3 volt. As the potential applied to a cell containing titanium dichloride and titanium trichl'oride dissolved in fused alkali chlorides is increased from an initial low value, no significant current passes through the electrolyte until the applied potential is sufficient to reduce the trichloride to dichloride and chlorine. Then as the potential is increased the current increases rapidly. At first the increase in current with further increase in applied potential is limited only by the'ohmic resistance of the bath and the cell components. However, as the current is further increased the cathode reaction is influenced by the rate at which trivalent titanium ions can diffuse to the cathode surface. After the current becomes equivalent to the rate at which trivalent titanium ions diffuse into the cathode layer, it changes little with increasing applied potential until the cathode becomes sufliciently polarized to permit the reduction of the dichloride to metallic titanium. Beyond this point the current again increases rapidly with increasing applied potential. Thus, to prevent the deposition of a significant quantity of metal on the auxiliary cathode, it is only necessary to.

prevent the polarization potential from reaching a value of about 0.3 volt above the surface-to-bath potential required to effect reduction of titanium trichloride totitanium dichloride. It is not necessary to have the surfaceto-bath potential at the auxiliary cathode as much as 0.3 volt lower than that of the deposition cathode.

It will be readily appreciated that the extent to which polarization occurs depends inter alia upon the concentration of the titanous chloride in the bath adjacent the cathodes, the relative proportionsof these titanous chlorides (the dichloride and the trichloride), the composition of the cathodes, the activity of the circulation of the bath adjacent the cathodes, the temperature of the bath and the value of the cathode surface current density. These many variables make it meaningless to express in the form of a numerical range the values of current density which should be maintained :at the auxiliary cathode in order to achieve the degree of polarization, and hence the cell control, characteristic of the practice of our invention. It is meaningful, however, to specify simply that the electrolyzing current should be distributed between the deposition andauxiliary cathodes so as to maintain substantially different current densities thereat, the lower current density prevailing at the auxiliary cathode and being such as to effect electrolytic reduction of titanium trichloride to titanium dichloride but insuflicient to develop such polarization as to effect electrolytic reduction of titanium dichloride to metallic titanium. The reduction of titanium trichloride to titanium dichloride can be determined and monitored by analyzing a sample of the main body portion B of the bath for its average titanium valence, an average valence of 2.5 to 2.2 indicating proper control of the minimum polarization required in the practice of our invention. The maximum value of the proper range of polarization is, of course, readily indicated by the deposition of metalcathode or as one of two or more auxiliary cathodes.

The distribution of electrolyzing current between the deposition and auxiliary cathodes can be effected either by electrical control exterior of the cell or 'by choice of cathode surface area, or by a combination of both means. We presently prefer to achieve the desired current distribution by the choice of cathode surface area. ample, a wire screen provides, for a given lateral area, a greater bath contact surface area than a smooth nonforaminous surface. Thus, we have found it to be particularly effective to form the separate auxiliary cathode structure, if used, from one or a plurality of layers of woven wire screen. The greater surface area of this screen, coupled with the fact that such an auxiliary cathode is advantageously positioned outside of the deposition cathode and therefore has a larger diameter than that of the presently preferred cylindrical deposi direct communication with one another through themedium of the bath therebetween. In this way the bath composition can be maintained substantially uniform adjacent thedeposition and auxiliary cathodes immersed in the bath. The uniformity of bath composition is facilitated by the absence of a physical barrier between the cathodes, thus permitting thermal convection currents to circulate unimpeded through the main body portion B of the molten salt bath. Additional circulation is afforded For exa "7 by the bubbling in of the titanium 'tetrachloride feed, either alone or in an inert carrier gas such as argon. A greater degree of circulation can also be provided with a mechanical stirrer.

melt was considered stripped when the current had dropped below 70 amperes. During stripping, no current was passed to the cell wall, because in the absence of titanium tetrachloride feed there was no need for valence Although the point of introduction of the titanium 5 control. The titanium metal was recovered from the tetrachloride feed into the cell bath has been shown in deposition cathodes and was found to total 5830 grams. the accompanying drawing to be located between the Of this, 4150 grams were coarser than 200 mesh (Tyler auxiliary and deposition cathodes, it must be understood Standard) and upon arc melting yielded an ingot of 106 that the location of this point is not critical. Thus, the Brinell. Although 22% of the current was passed to the practice of our invention embraces the introduction of cell wall, only 5.2% of the recovered metal was not on the titanium tetrachloride adjacent either or both of the the deposition cathodes. auxiliary and deposition cathodes, or at a point intermediate these .cathodes, or at a point beyond the distal Example H surface of the auxiliary cathode, or at a remote point The Same cell arrangement, desmbed m,EXamP1e I such as in a separate 'body ofthe molten bath maintained used F Q that h mamum tetftmhlonde outside of the main body of the bath in an adjoining to a portion intermedlate the depositlon and auxlliary wenpor eveninra separate vesseL cathodes and that a separate auxiliary cathode was pro- The following specific examples are illustrative of vlded 1n the form of two sheets of n1ckel w1re cloth (4 the practice of ourinvention: meshes per lineal mob and 0.08 inch dlameter wire).

One sheet extended along the entire cell wall, spaced one Example! inch inwardly therefrom, and the other sheet was coex- A rectangular cell was partially filled with pre-dried tensive with the first but spaced inwardly /2 inch thereeutectic melt. Two cylindrical deposition cathodes of a from. The current to the deposition cathodes was divided corrosion-resistant nickel base alloy were perforated equally between the two. The current to the auxiliary to the extent of 42% of their effective area and were lined cathodes (one comprising the cell wall and the other with a fine mesh screen. These cathodes were spaced the two screens) was divided on the basis of relative suralong the long dimension of the cell. A graphite anode face area, approximately two-thirds to the screens and onerod was centered in each of the deposition cathodes. third to the cell wall. Titanium tetrachloride was fed to Titanium tetrachloride was fed below the melt surface the cell essentially as rapidly as the melt would accept it using argon as a carrier. The feed pipe was placed in during the early stages of build-up. The current to the juxtaposition with one of the deposition cathodes. The deposition cathodes was maintained near the minimum bath temperature was maintained at 600 C. during permitting good control of the cell until a titanous build-up of the titanous chloride concentration and at chloride concentration of more than 2% titanium and 550 C. during steady-state and stripping periods. The a valence of less than 2.4 had been established. Since the titanium product was harvested at 450 C. titanium tetrachloride was fed very rapidly in the early A titanous chloride concentration of 2.26% titanium stages of build-up, there was a period of 1% hour near at an average valence of 2.58 was established in a 12% the end of this stage in which current was passed in the hour period during which 1927 ampere-hours were passed absence of further titanium tetrachloride feed so as to through the cell and titanium tetrachloride equivalent to bring the current and feed in balance for theoretical reduc- 1930 grams of titanium was fed into the cell. During 4 tion to TiCl During this latter period, electrochemical this stage, 43.4% of the current was passed to the cell action was primarily limited to the reduction of TiCl to wall as the auxiliary cathode and the balance was divided TiCl as evidenced by only a minor decrease in concenbetween the two deposition cathodes. In the steady-state tration from 2.66 to 2.59% titanium while the average period of hours which followed, titanium tetravalence decreased from 2.76 to 2.45. During the buildchloride equivalent to 4280 grams of titanium was fed up period, 83% of the current was passed to the auxiliary at a rate approximately in balance with the current for cathodes. theoretical reduction to metal, and of the 9765 ampere- During the steady-state period, the titanium tetrachlohours passed during this period 26.9% went to the cell ride feed was essentially in balance with the current for wall. During the first 8 hours of steady-state operation, theoretical reduction to metal. For the first 8 hours of the valence dropped to 2.36 and remained at this level for steady-state operation, the current distribution described the remainder of this stage. After completion of the for the latter partof the build-up period was maintained steady-state period, the melt was essentially stripped of to achieve a further reduction in valence to 2.33. During soluble titanium values in 17 hours by passing 2066 the balance of steady-state operation, with 57% of the ampere-hours to the deposition cathodes. The total current going to the deposition cathodes, the valence current was held constant until an open circuit (back) dropped more slowly to 2.28. The stripping procedure E.M.F. of 3.2 volts indicated that the titanous chloride was substantially the same as in Example I. Details concentration was low. The current was then gradually of the current distribution during the entire operation are reduced to maintain this open circuit voltage, and the set forth in the following table:

Deposition Auxiliary Cathodes Oathodes (Two) (Cell Wall and TiOlr Feed Av. Total Screen) Time Interval Current Av.An1p. l i e d Av.Amp. l itifi cc/Hr i e Amp-hr. Amp-hr. Faraday Concentration Build-up:

1 Hr 90 25 25 65 600 l. 6 179 45 134 199 600 0. 8 271 60 211 410 see 0. 7 377 so 317 727 800 0. s 395 60 355 335 1, e53 840 0. 5 402 60 430 342 2,081 0 0 39s 60 910 33s 4, 732 399 o. 24 405 231 4, 727 174 7, 051 406 0. 24

Of the 5390 grams of metal recovered from the deposition cathodes pursuant to the foregoing operation, 4940 grams were coarser than 200 mesh and yielded an arcmelted ingot of 93 Brinell. Although only 57% of the current was passed to the deposition cathodes, 92% of the recovered metal was obtained from them.

We claim:

1. In the electrolysis between an anode and a cathode of a fused halide salt bath containing titanium trichloride and titanium dichloride wherein titanium tetrachloride is substantially continuously introduced into and assimilated by the bath and metallic titanium is deposited on the cathode immersed in the bath, the titanium tetrachloride being introduced into the portion of the bath in contact with the surface of the cathode distal with respect to the anode and the portion of the bath between the anode and the proximate cathode surface being substantially completely depleted of titanium ions so that the metallic titanium is deposited primarily on the aforesaid distal surface of the cathode, the anode and the deposition cathode being in direct fluid contact with one another through the medium of the bath therebetween, the improvement which comprises effecting circulation of the bath in contact with the distal surface of the deposition cathode so as to maintain substantially uniform concentrations of the titanium trichloride and titanium dichloride in all portions of the bath which are adjacent said distal surface and an auxiliary cathode also in contact with the bath, the auxiliary cathode being in direct communication with the deposition cathode through the medium of the bath therebetween, the cell atmosphere above the deposition cathode being in direct communication with the cell atmosphere above the auxiliary cathode, distributing the electrolyzing current between the deposition and auxiliary cathodes so as to maintain substantially different current densities thereat, the current density at the auxiliary cathode being such as to efiect electrolytic reduction of titanium trichloride to titanium dichloride but insufiicient to develop such polarization as to effect significant electrolytic reduction of titanium dichloride to metallic titanium, the resulting titanium dichloride being available substantially throughout the bath in contact with both cathodes for chemical reaction with the titanium tetrachloride introduced into the bath and present also in the atmosphere thereabove with resulting production in situ in the bath of the titanium trichloride which is electrolytically reduced to dichloride at the auxiliary cathode.

2. In the electrolysis between an anode and a cathode of a fused halide salt bath containing titanium trichloride and titanium dichloride wherein titanium. tetrachloride is substantially continuously introduced into and assimilated by the bath and metallic titanium is deposited on the cathode immersed in the bath, the titanium tetrachloride being introduced into the portion of the bath in contact with the surface of the cathode distal with respect to the anode and the portion of the bath between the anode and the proximate cathode surface being substantially completely depleted of titanium ions so that the metallic titanium is deposited primarily on the aforesaid distal surface of the cathode, the anode and the deposition cathode being in direct fluid contact with one another through the medium of the bath therebetween,

the improvement which comprises effecting circulation of the bath in contact with the distal surface of the deposition cathode so as to maintain substantially uniform concentrations of the titanium trichloride and titanium dichloride in all portions of the bath which are adjacent said distal surface and an auxiliary cathode also in contact with the bath, the average valence of the titanium ions in the bath being within the range of 2.5 to 2.2, the auxiliary cathode being in direct communication with the deposition cathode through the medium of the bath therebetween, the cell atmosphere above the deposition cathode being in direct communication with the cell atmosphere above the auxiliary cathode, distribut- '10 auxiliary cathodes so as to maintain substantially dif ferent current densities thereat, the current density at the auxiliary cathode being such as to effect electrolytic reduction of titanium trichloride to titanium dichloride but insuflicient to develop such polarization as to effect significant electrolytic reduction of titanium dichloride to metallic titanium, the resulting titanium dichloride being available substantially throughout the bath in contact with both cathodesfor chemical reaction with the titanium tetrachloride introduced into the bath and'present also in the atmosphere thereabove with resulting production in situ in the bath of the titanium trichloride which is electrolytically reduced to dichloride at the auxiliary cathode.

3. In the electrolysis between an anode and a cathode of a fused halide salt bath containing titanium trichloride and titanium dichloride wherein titanium tetrachloride is substantially continuously introduced into and assimilated by the bath and metallic titanium is deposited on the cathode immersed in the bath, the titanium tetrachloride being introduced into the portion of the bath in contact with the surface of the cathode distal with respect to the anode and the portion of the bath between the anode and the proximate cathode surface being substantially completely depleted of titanium ions so that the metallic titanium is deposited primarily on the afore said distal surface of the cathode, the anode and the deposition cathode being in direct fluid contact with one another through the medium of the bath therebetween, the improvement which comprises effecting circulation of the bath in contact with the distal surface of the deposition cathode so as to maintain substantially uniformconcentrations of the titanium trichloride and titanium dichloride in all portions of the bath which are adjacent said distal surface and an auxiliary screencathode similarly immersed in the bath, the auxiliary cathode being in direct communication with the deposition cathode through the medium of the bath therebetween, the cell atmosphere above the deposition cathode being in direct communication with the cell atmosphere above the auxiliary cathode, distributing the electrolyzing current between the deposition and auxiliary cathodes so as to maintain substantially different current densities thereat, the current density at the auxiliary cathode being such as to effect electrolytic reduction of titanium trichloride to titanium dichloride but insufiicient to develop such polarization as to effect significant electrolytic reduction of titanium dichloride to metallic titanium, the resulting titanium dichloride being available substantially throughout the bath in contact with both cathodes for chemical reaction with the titanium tetrachloride introduced into the bath and present also in the atmosphere thereabove with resulting production in situ in the bath of the titanium trichloride which is electrolytically reduced to dichloride at the auxiliary cathode.

4. In the electrolysis between an anode and a cathode of a fused halide salt bath containing titanium trichloride and titanium dichloride wherein titanium tetrachloride is substantially continuously introduced into and assimilated by the bath and metallic titanium is deposited on the cathode immersed in the bath, the titanium tetrachloride being introduced into the portion of the bath in contact with the surface of the cathode distal with respect to the anode and the portion of the bath between the improvement which comprises eifecting circulation of the bath in contact with the distal surface of. the deposition cathode so as to maintain substantially uniform concentrations ofthe titanium trichloride and titanium dichloride in all portions of the bath which are ing the electrolyzing current between the deposition and adjacent said distal surface and an auxiliary cathode also in contact with the ,bath, the auxiliary cathode being in direct communication with the deposition cathode through the medium of the bath therebetween, the cell atmosphere above the deposition cathode being in direct communication with the cell atmosphere above the auxiliary cathode, distributing the electrolyzing current between the deposition and auxiliary cathodes so as to maintain substantially different current densities thereat, the current density at the auxiliary cathode being such as to eifect electrolytic reduction of titanium trichloride to titanium dichloride with a resulting average titanium valence of 2.5 to 2.2 in the portion of the bath adjacent the deposition and auxiliarycathodes but insufficient to develop such polarization as to effect electrolytic reduction of titanium dichloride to metallic titanium to such extent as to produce at the auxiliary cathode as much as 15% of the total metallic titanium recovered, the resulting titanium dichloride being available substantially throughout the bath in contact with both cathodes for chemical reaction with the titanium tetrachloride introduced into the bath and present also in the atmosphere thereabove with resulting production in situ in the bath of the titanium trichloride which is electrolytically reduced to dichloride at the auxiliary cathode.

5. In the electrolysis between an anode and a cathode of a fused halide salt bath containing titanium trichloride and titanium dichloride wherein titanium tetrachloride is substantially continuously introduced into and assimulated by the bath and metallic titanium is deposited on the cathode immersed in the bath, the titanium tetrachloride being introduced into the portion of the bath in contact with the surface of the cathode distal with respect to the anode and the portion of the bath between the anode and the proximate cathode surface being substantially completely depleted of titanium ions so that the metallic titanium is deposited primarily on the aforesaid distal surface of the cathode, the anode and the deposition cathode being in direct fluid contact with one another through the medium of the bath therebetween, the improvement which comprises efiecting circulation of the bath in contact with the distal surface of the deposition cathode so as to maintain substantially uniform concentrations of the titanium trichloride and titanium dichloride in all portions of the bath which are adjacent said distal surface and an auxiliary cathode assembly comprising the cell wall and a separate auxiliary screen cathode immersed in the bath, the auxiliary cathode being in direct communication with the deposition cathode through the medium of the bath therebetween, the cell atmosphere above the deposition cathode being in direct communication with the cell atmosphere above the auxiliary cathode, distributing the electrolyzing current between the deposition and auxiliary cathodes so as to maintain substantially different current densities thereat, the current density at the auxiliary cathode being such as to effect electrolytic reduction of titanium trichloride to titanium dichloride but insufficient to develop such polarization as to efiect significant electrolytic reduction of titanium dichloride to metallic titanium, the resulting titanium dichloride being available substantially throughout the bath in contact with both cathodes for chemical reaction with the titanium tetrachloride introduced into the bath and present also in the atmosphere thereabove with resulting production in situ in the bath of the titanium trichloride which is electrolytically reduced to dichloride at the auxiliary cathode.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE ELECTROLYSIS BETWEEN AN ANODE AND A CATHODE OF A FUSED HALIDE SALT BATH CONTAINING TITANIUM TRICHLORIDE AND TITANIUM DICHLORIDE WHEREIN TITANIUM TETRACHLORIDE IS SUBSTANTIALLY CONTINUOUSLY INTRODUCED INTO AND ASSIMILATED BY THE BATH AND THE METALLIC TITANIUM IS DEPOSITED ON THE CATHODE IMMERSED IN THE BATH, THE TITANIUM TETRACHLORIDE BEING INTRODUCED INTO THE PORTION OF THE BATH IN CONTACT WITH THE SURFACE OF THE CATHODE DISTAL WITH RESPECT TO THE ANODE AND THE PORTION OF THE BATH BETWEEN THE ANODE AND THE PROXIMATE CATHODE SURFACE BEING SUBSTANTIALLY COMPLETELY DEPLETED OF TITANIUM IONS SO THAT THE METALLIC TITANIUM IS DEPOSITED PRIMARILY ON THE AFORESAID DISTAL SURFACE OF THE CATHODE, THE ANODE AND THE DEPOSITION CATHODE BEING IN DIRECT FLUID CONTACT WITH ONE ANOTHER THROUGH THE MEDIUM OF THE BATH THEREBETWEEN, THE IMPROVEMENT WHICH COMPRISES EFFECTING CIRCULATION OF THE BATH IN CONTACT WITH THE DISTAL SURFACE OF THE DEPOSITION CATHODE SO AS TO MAINTAIN SUBSTANTIALLY UNIFORM CONCENTRATIONS OF THE TITANIUM TRICHLORIDE AND TITANIUM DICHLORIDE IN ALL PORTIONS OF THE BATH WHICH ARE ADJACENT SAID DISTAL SURFACE AND AN AUXILIARY CATHODE ALSO IN CONTACT WITH THE BATH, THE AUXILIARY CATHODE BEING IN DIRECT COMMUNICATION WITH THE DEPOSITION CATHODE THROUGH THE MEDIUM OF THE BATH THEREBETWEEN, THE CELL ATMOSPHERE ABOVE THE DEPOSITION CATHODE BEING IN DIRECT COMMUNICATION WITH THE CELL ATMOSPHERE ABOVE THE AUXILIARY CATHODE, DISTRIBUT- 